Radegast den

A famous Czech beer, in honor of a Slavic god, Radegast, the god of hospitality, has recently had its day: Radegast den (Radegast or Radegast's day). This construction seems to be an English calque. Czech would require the noun to be in the genitive form: Radegastův den or Den Radegasta. English seems to be creeping in not only in the lexicon of the language, but also more stealthily in its syntax.